Various forms of sound attenuating earcups are known from the prior art for protecting the ear of the wearer from the effects of ambient noise. For example, the crew of rotary wing aircraft are provided with earcups used in combination with protective helmets. The helmets are equipped with an oversized earcup-receiving dome wherein the earcup may be adjustably located to custom fit the wearer. Usually such helmets are equipped with earphones and microphones to allow communication with the wearer. Typically these helmets equipped with earphones must possess the adjustability to fit a specified anthropometric range, yet provide exceptional noise attenuation and adequate communication capabilities.
Previous attempts to fulfill these various objectives may be seen in four prior art patents owned by the assignee of this application. U.S. Pat. No. 3,875,592 discloses a contoured cup surface which compliments the shape of the wearer's head surrounding the ear. The ear seal has a uniform thickness that follows the contour of the cup to provide a highly effective seal with the wearer's head at all points around the ear. U.S. Pat. No. 4,700,410 provides an inflatable bladder between the earcup and helmet to bias the earcup against the wearer's head. U.S. Pat. No. 5,020,163 discloses a resilient annular earseal having an inner preferral portion projecting outwardly toward the wearer's head. While these designs are effective in providing better seals, they do not provide adequate attenuation of ambient noise, particularly in the low frequencies. U.S. Pat. No. 5,148,887 discloses a moveable piston within the earcup which responds to ambient noise impinging on the shell to maintain the internal volume substantially constant. While this patent provides better attenuation of ambient noise, its design along with the inflatable bladder design are complex and therefor expensive to produce.
Accordingly it would be desirable to provide an earcup assembly for use in conjunction with an aircrew helmet which is simple in design, provides improved sound attenuation and communication capabilities and is easily custom fit to individual crew members.